Browsing by Author "Soumitra Paul Chowdhury"

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Diversity of 16S-rRNA and nifH genes derived from rhizosphere soil and roots of an endemic drought tolerant grass, Lasiurus sindicus
(2009) Soumitra Paul Chowdhury; Michael Schmid; Anton Hartmann; Anil Kumar Tripathi
Lasiurus sindicus is a highly nutritive, drought tolerant, perennial grass, endemic to the Thar Desert of Rajasthan, India. In order to characterize the diversity of bacteria associated with roots of this grass that had survived severe drought stress, 16S-rRNA gene clone libraries were established from RT-PCR amplified products of the total RNA extracted from the washed roots and rhizosphere soil samples. Eight major bacterial taxa were identified in a total of 121 16S-rRNA gene clones. The majority of sequences belonged to Gram-positive bacteria, Actinobacteria being the most predominant ones, closely followed by Firmicutes. Most of the sequences showed similarity with sequences from cultivated bacteria or uncultivated environmental clones associated with arid, semi-arid environments, cold deserts and contaminated soils. PCR amplification of nifH genes using total DNA as template produced a total of 48 nifH clones from the rhizosphere soil and root samples and revealed a predominance of nifH sequences closely affiliated to Pseudomonas pseudoalcaligenes, isolated in a previous study from root samples of Lasiurus sindicus. Some nifH sequences showed close similarity to cultivated diazotrophs like Azospirillum brasilense, Rhizobium sp., and a variety of uncultured nitrogen fixing bacteria. Thus, this study provides us with evidence that L. sindicus harbors a diversity of bacteria with potential for nitrogen fixation. © 2008 Elsevier Masson SAS. All rights reserved.
Endophytic colonization ability of two deep-water rice endophytes, Pantoea sp. and Ochrobactrum sp. using green fluorescent protein reporter
(2004) Subhash C. Verma; Anamika Singh; Soumitra Paul Chowdhury; Anil K. Tripathi
Colonization ability of the two endophytic bacteria, isolated from surface sterilized seeds of Jaisurya variety of deep-water rice viz., Pantoea sp. and Ochrobactrum sp., was compared after genetically tagging them with a constitutively expressing green fluorescent protein gene (gfp). Confocal laser scanning microscopy (CLSM) of hydroponically grown seedlings of Jaisurya rice, inoculated with gfp-tagged endophytes, revealed that both Pantoea sp. and Ochrobactrum sp. colonized the intercellular spaces in the root cortex when inoculated separately. Colonization by gfp-tagged Ochrobactrum sp. was severely inhibited when co-inoculated with an equal number (105 c.f.u. ml -1) of wild type Pantoea sp., but the converse was not true. Pantoea sp. was a more aggressive endophytic colonizer of its host than Ochrobactrum sp. The potential of using GFP reporter and CLSM as tools in evaluating competitive ability of colonization among endophytes is herewith demonstrated.
Identification of diazotrophs in the culturable bacterial community associated with roots of Lasiurus sindicus, a perennial grass of Thar Desert, India
(2007) Soumitra Paul Chowdhury; Michael Schmid; Anton Hartmann; Anil Kumar Tripathi
Lasiurus sindicus is a highly nutritive, drought-tolerant, perennial grass that is endemic to the Thar Desert of Rajasthan, India. Analysis of 16S rRNA coding genes of the bacterial isolates enriched in nitrogen-free semisolid medium, from the surface-sterilized roots of L. sindicus, showed predominance of Gram-negative over Gram-positive bacteria. According to comparative sequence analysis of 16S rDNA sequence data, Gram-positive bacteria with low GC content (Staphylococcus warneri and Bacillus sp.) and high GC content (Micrococcus luteus, Microbacterium sp.) were identified. Gram-negative bacteria included Azospirillum sp., Rhizobium sp., Agrobacterium tumefaciens, and Inquilinus limosus (α-proteobacteria); Ralstonia sp., Variovorax paradoxus, and Bordetella petrii (β-proteobacteria); and Pseudomonas pseudoalcaligenes, Stenotrophomonas sp. (γ-proteobacteria). The occurrence of nifH sequences in Azospirillum sp., Rhizobium sp., and P. pseudoalcaligenes showed the possibility of supplying biologically fixed nitrogen by the root-associated diazotrophs to the host plant. © 2007 Springer Science+Business Media, LLC.
Ochrobactrum oryzae sp. nov., an endophytic bacterial species isolated from deep-water rice in India
(2006) Anil K. Tripathi; Subhash C. Verma; Soumitra Paul Chowdhury; Michael Lebuhn; Andreas Gattinger; Michael Schloter
A non-pigmented, motile, Gram-negative bacterium designated MTCC 4195T was isolated from surface-sterilized seeds and plant tissue from deep-water rice (Oryza sativa) cultivated in Suraha Tal Lake in northern India. This isolate was shown to reinfect and colonize deep-water rice endophytically. The highest level of 16S rRNA sequence similarity (96.8 %) to strain MTCC 4195T was shown by Ochrobactrum gallinifaecis DSM 15295T. Strain MTCC 4195T utilized γ-hydroxybutyric acid, adonitol, D-glucosaminic acid and arabinose as carbon sources, but failed to use gentiobiose or citrate. The cell-wall fatty acids of strain MTCC 4195T were characterized by the presence of a relatively large proportion of C18:1ω7c and a relative small proportion of C16:0 in comparison with Ochrobactrum species. DNA-DNA relatedness studies showed less than 52 % binding with the DNAs of type strains of other species of the genus Ochrobactrum. On the basis of phenotypic and genotypic characteristics and the results of 16S rRNA gene sequence analysis, the novel species Ochrobactrum oryzae sp. nov. is proposed, with MTCC 4195T (= DSM 17471T) as the type strain. © 2006 IUMS.
Phylogeny based on 16S rDNA and nifH sequences of Ralstonia taiwanensis strains isolated from nitrogen-fixing nodules of Mimosa pudica, in India
(2004) Subhash Chandra Verma; Soumitra Paul Chowdhury; Anil Kumar Tripathi
Bacterial symbionts present in the indeterminate-type nitrogen (N)-fixing nodules of Mimosa pudica grown in North and South India showed maximum similarity to Ralstonia taiwanensis on the basis of carbon-source utilization patterns and 16S rDNA sequence. Isolates from the nodules of M. pudica from North India and South India showed identical ARDRA (Amplified Ribosomal DNA Restriction Analysis) patterns with Sau3AI and RsaI, but AluI revealed dimorphy between the North Indian and South Indian isolates. Alignment of 16S rDNA sequences revealed similarity of North Indian isolates with an R. taiwanensis strain isolated from M. pudica in Taiwan, whereas South Indian isolates showed closer relatedness with the isolates from Mimosa diplotricha. Alignment of nifH sequences from both North Indian and South Indian isolates with that of the related isolates revealed their closer affinity to α-rhizobia, suggesting that nif genes in the β-rhizobia might have been acquired from α-rhizobia via lateral transfer during co-occupancy of nodules by α-rhizobia and progenitors of R. taiwanensis, members of the β-subclass of Proteobacteria. Immunological cross-reaction of the bacteroid preparation of M. pudica nodules showed strong a positive signal with anti-dinitrogenase reductase antibody, whereas a weak positive cross-reaction was observed with free-living R. taiwanensis grown microaerobically in minimal medium with and without NH4Cl. In spite of the expression of dinitrogenase reductase under free-living conditions, acetylene reduction was not observed under N-free conditions even after prolonged incubation.
Strain-specific salt tolerance and osmoregulatory mechanisms in Azospirillum brasilense
(2007) Soumitra Paul Chowdhury; Thirunavukkarasu Nagarajan; Rachna Tripathi; Mukti Nath Mishra; Daniel Le Rudulier; Anil Kumar Tripathi
Salinity stress inhibits the growth and nitrogen fixation ability of the plant growth-promoting rhizobacterium Azospirillum brasilense. Five strains of A. brasilense were isolated from the rhizosphere of Indian cereals and grasses and identified on the basis of their phenotypic features and 16S rRNA gene sequence. The five Indian isolates and two standard strains of A. brasilense, Sp7 and Cd, showed notable differences in growth, acetylene-reducing activity under salt stress, and ability to take up and use glycine betaine for the restoration of growth and acetylene-reducing activity under salt stress. Salt stress also enhanced the production of exopolysaccharides and cell aggregates, the extent of which varied in different strains of A. brasilense at different carbon to nitrogen ratios in the culture medium. It can be concluded that the production of exopolysaccharides and cell aggregates is a more consistent physiological response of A. brasilense to salt stress than is the uptake and osmoprotection by glycine betaine. © 2006 Federation of European Microbiological Societies.